An investigation of manual transmission drive rattle

Manual transmission gear rattle is an NVH (noise, vibration, and harshness) concern in the automotive industry. It is induced by repetitive impacts on loose (unselected) gear wheel teeth by their corresponding driving pinions. This phenomenon occurs under various loading conditions and is classified accordingly, including ‘idle rattle’ when the transmission is in neutral and ‘creep and drive rattle’ when the transmission is in a gear with a widely open or a partially open throttle. The phenomenon is also present from drive to coast conditions, referred to as overrun rattle. Engine order fluctuations on the input shaft are considered to be the underlying cause for rattle of loose gears. However, the mechanism of transmission of vibration through lubricated contacts is not fundamentally understood. It is surmised that changes in lubricated contact conditions at different bulk oil temperatures may play a key role and, therefore, offer an opportunity to deal with rattle by a root-cause fundamental solution. This means that a detailed multi-physics approach (including dynamics, vibration, and tribology) is needed. This article provides detailed analytical models of lubricated conjunctions in a multi-body dynamics model of a transaxle seven-speed transmission system under creep rattle conditions. The results show the important role of the regime of lubrication in lightly loaded conjunctions, increasing the propensity to rattle at higher temperatures. It is also revealed that the effect of engine order vibration as an initiating source for rattle becomes significant with reduced hydrodynamic contact stiffness at rising temperatures.